feat : implement empty States for Metric Charts

[Bhenzdizma]

This PR improves the analytics empty state for newly signed-up merchants whose charts previously appeared blank or displayed awkward axes when no real data was available.

What Changed

• Added an engaging empty state layout for merchant charts
• Rendered a faint/dotted example curve to make the chart area feel intentional and visually informative
• Added a clear call-to-action:
  "Create your first payment link to see metrics"

Why

For new merchants with no transaction data yet, the chart area could look broken, confusing, or empty. This update makes the dashboard feel more polished and helps guide first-time users toward the next meaningful action.

Result

• Prevents blank or strange-looking chart states for new users
• Improves first-time dashboard experience
• Encourages activation by directing merchants to create their first payment link

Notes

This change only affects the no-data / new-user chart state and does not alter the behavior of charts when real metrics are available.

closes #383
closes #384

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